Production of lower valent halides



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PRODUCTION OF LOWER VALENT HALIDES Eugene Wainer, Cleveland Heights, Ohio, assignor by mesne assignments, to Horizons Titanium Corporation, Princeton, N. J., a corporation of New Jersey No Drawing. Application May 16, 1956 Serial No. 585,171

11 Claims. (Cl. 75-1) This invention relates to the produce of lower valent halides of certain polyvalent transition metals from which the metals themselves may be obtained either by subsequent disproportionation of the lower valent metal halide or by electrolytic decomposition of the lower valent metal halide while dissolved in or assimilatedby a fused salt bath.

Because of the possibilities inherent in the production of various transition metals either by electrolytic decomposition or by disproportionation of their lower valent halides, considerable attention has been devoted heretofore to the production of these lower valent halides. For this purpose, numerous reducing agents such as hydrogen and various metals have been proposed and used, but it has been characteristic of such procedures that a significant portion of the halogen component of the initial transition metal halide has been lost by its com bination with the reducing agent. Consequently, the amount of lower valent transition metal halide thus produced has always been less than the starting amount of the higher valent transition metal halide. The use of the transition metal itself as a reducing agent has been proposed and explored, but the inherent disadvantage in this procedure is that it is predicated upon the previous production of the transition metal itself.

I have now discovered that the lower valent halides of the multivalent transition metals vandium, niobium, tantalum, titanium, zirconium and hafnium may be obtained by reaction between the higher valent simple halides of the metals and the lower valent simple sulfides,

of these metals. The method of my invention for producing the lower valent halides of these metals comprises bringing the higher valent simple halide of the metal in the vapor state into contact with a mass of the lower valent simple sulfide of one of these metals in the form of particles at least as fine as about 200 mesh, and effecting reaction between the higher valent metal halide and the lower valent sulfide by maintaining the reactants at a temperature at least as high as the volatilization temperature of the higher valent metal halide but below that at which the resulting lower valent metal halide .disproportionates to the metal itself. I have further discovered that if the resulting lower valent transition metal halide is heated to a temperature at which it will disproportionate to form the transition metal itself, the combination of these steps results in a process wherein the transition metal sulfide is converted to the transition metal itself without consumption ofthe transition metal higher valent halide.

The higher valent halides of the aforementioned transition metals useful in practicing the invention comprise the simple chlorides, bromides, iodides or fluorides provided that they are sufilciently volatile to permit their reaction with the lower valent sulfide in the substantially dry state, i. e. in the substantial absence of a molten phase, at temperatures below those at which the corresponding lower valent halide disproportionates. In general, these higher valent halides which are readily vola- 2,833,541 Patented May 6, I958 Ia tile are the tetravalentqhalides, although in the case of vanadium, higher valent halides such as the pentavalent and hexavalent halides are suitable. All of these metal halides are available in a state of purity adequate for the practice of my invention, but if desired, these halides may be further purified by distilling or subliming them into the reaction zone, or by any other appropriate purification procedure.

The transition metal simple sulfide used in the practice of my invention should be of high purity. That is, it should be free of contaminants which would otherwise be carried over into the lower valenthalide product. High purity transition metal sulfides can be produced either by reacting the transition metal halides with hydrogen sulfide at appropriate elevated temperatures or by heating the impure transition metal with elemental sulfur under a controlled atmosphere. In the event that the metal is one which combines to form more than one simple sulfide, the transition metal simple sulfide selected should be one in which the transition metal exhibits a lower valence than the maximum valence of the transition metal. For example, in the case of titanium, three sulfides are known, namely, titanium disulfide, titanium sesquisulfide, and titanium monosulfide. In the practice of my invention only the latter two sulfides may be used, and where a divalent titanium halide is to be, obtained, only the divalent sulfide, titanium monosulfide can be used.

In general, whatever the transition metal sulfide employed, it should be chosen from sulfides in which the valence of the transition metal is no higher than the valence of the transition metal in the lower valenttransition metal halide to be produced.

The transition metal simple sulfide should be in a finely divided form in order to promote reaction between the sulfide and the transition metal higher valent halide. In general, I have found. it advisable to use a sulfide particle size at least as fine as about 200 mesh (Tyler Standard). The reaction. between the higher valent transition metal halide and the transition metal sulfide takes place readily at elevated temperatures when the vapors of the halide are passed. over or through a mass of the finely divided sulfide. The reaction vessel, such as a quartz-lined furnace, should be gas-tight so that its atmosphere may be evacuated, then flushed with an inert gas such as argon and finally re-evacuated prior to the introduction of the transition metal higher valent halide. The reaction vessel is also advantageously provided with an outlet communicating with a closed condensing system in which the lower valent transition metal halide product may be liquiefied or solidified if the reaction temperature is above the normally liquid or solid state of the lower valent halide product.

In a continuous process, any unconsumed higher valent metal halide leaving the furnace may be separated from the sulphur halide by bubbling through an appropriate solvent for the latter, such as carbon disulphide, in which the higher valent halide is insoluble and with which it does not react.

The reaction temperatures at which the lower valent halides of the aforementioned polyvalent transition metals 0,. Vanadium 300- 800 Niobium 400- 900 Tantalum 400- 900 Titanium 300- 800 Zirconium 600-1100 Hafnium 600-l 100 Within each of these ranges, higher temperatures promote more rapid reaction rates for each specific halide-sulfide reaction. In reactions wherein'the lower valent halide product is not normally solid or liquid, increased pressure in the reaction zone will permit the use of a higher operating temperature while maintaining the same equilibrium as that prevailing at lower temperature and normal pressure. Accordingly, superatmospheric pressures may be used advantageously in the reaction zone in order to promote more rapid rate of the conversion of the higher valent transition metal halide to the lower valent halide.

'The lower valent transition metal halide produced by the practiceof my invention is generally the trivalent halide, although this halide is frequently accompanied by other lower valent halides. Within the effective operating temperature range for each transition metal halide, lower temperatures tend to promote the formation of halides having a lower valence thanthe halides produced at the higher operating temperatures. For example, in producing the lower halides of titanium from the tetrahalide of titanium, titanium trihalide formation is favored by reaction temperatures of about 500-800 C. But by loweringthe temperature below this operating range, that is, by using a temperature of about 300400 C. at subatmospheric pressure, the dihalide of titanium predominates in the reaction product. Thus, by using a temperature range near or even below the optimum tempera tureranges set forth hereinbefore, and by further using subatmospheric pressures, the reaction may be made to proceed effectively. with the production of the lowest valent. halides'of each polyvalent transition metal, although generally, this result is achieved at the expense of lower reaction efiiciency,

When the reaction isv carried out in the manner above described, instead of a conventional condensing system, I have found it to be particularly advantageous to pass the products evolved directly into a fused salt bath, preferably one composed'essentially of one or more alkali metal halides, of a composition which forms a'stable,

fluid melt at the desired temperature. Sodium chloride, and mixtures of sodium chloride and potassium chloride have been employed successfully for this purpose. The resulting fused salt product has been found to be admirably suited to the production of the desired metal by means of a used salt electrolytic decomposition of the bath.

When the reaction is carried out in a closed bomb type reaction vessel, I prefer to leach the product, to first effect removal of any sulfur or soluble sulfides present employing ordinary carbon disulphide. The insoluble residue is then treated with a fused alkali metal halide melt in which the lower valent metal halides dissolve, and in which the original sulfides have only the most limited solubility. This treatment is carried out under an inert atmosphere, such as argon, to avoid any reoxidation of the lower valent halide reaction product. Where-significant amounts of the insoluble portions ofthe reaction mass are physically carried into the fused halide salt, a fairly good separation can be obtained by permitting the fused salt product to stand at an elevated temperature and then decanting the melt, thereby obtaining a clean electrolyte from which the transition metal is recoverable by techniques known in the art.

' The following examples are illustrative of the practice of-my invention for the production of lower valent halides of the aforementioned transition metals:

l mesa;

Example I A silica tube furnace, equipped with a vacuum-tight water cooled head was used as the reaction vessel. A boat containing 200 gins. of minus 200 mesh high purity titanium monosulfide was inserted in the furnace and the unit was sealed and evacuated. The furnace was heated to a temperature of about 550 C. and titanium tetrachloride was then distilled into the reactor at a rate suflicient to maintain a reaction zone pressure of about one atmosphere. After four hours at 750 C., the furnace was cooled while maintaining a titanium tetrachloride pressure of one atmosphere until the furnace temperature was below the normal boiling point of titanium tetrachloride. The furnace was then opened, and the reacted mass was removed and leached with aqueous l N hydrochloric acid. After filtration, an aqueous solution of pure titanium trichloride was obtained.

Example 11 The reaction was conducted as in Example I until the cooling stage was reached. At this time the flow of tetrachloride was stopped, argon was introduced into the furnace to flush out any gases present, and the furnace was evacuated'to a pressure of l0 atmospheres and cooled. The reaction mass contained titanium dichloride together with sulfur and traces of unreacted titanium The titanium dichloride product was re 1 monosulfide. covered in a form suitable for the electrolytic production Qftit-anium by leaching the reaction product mass witha molten mixture of sodium chloride and potassium chloride. The yield of titanium dichloride was substantially quantitative based on the titanium monosulfide originally present in the charge.

Example III Example IV Zirconium sulfide and zirconium tetrachloride were reacted as described in. Example I. The reaction temperature was held at about 800 C. Substantially a yield of zirconium trichloride was obtained.

Although the lower valent transition metal halides produced by the practice of my invention may be used as a source of the transition metal supply for fused salt bath electrolytic production of the transition metal itself, I have found that the combination of my novel method of producing the lower valent metal halides with subsequent disproportionation of the lower valent halide to the metal results in a process wherein the transition metal sulfide is converted to the metallic state. The result can be visualized by the following representative equations in which M represents the transition metal, X represents a halogen and S is sulfur:

16MX4 4MB ZOMX;

LlOMXz MXi nus 2MXa MX: S

MX: MX4

M lVIXt Regardless of. which reaction course. is actually representative of the combination of steps by which I produce the transition metal. itself, it will be seen that the reactions involve the conversion. of the higher valent transition metal halide to. a lower valent halide-and .that \subsequent'reaction:effects conversion of the lowervalent halide to'the metal itself by disproportionation. In. the tourse of these two-basic steps, and regardless of whether hese reactions or other reactions are written to represent he course of events, it will be seen that the disproportionation reactions regenerate much of the higher valent trinsition metal halide initially reacted with the transimetal sulfide and that. in some instances, complete regeneration is-obtained. Thus, the higher valent transition'metal halide is-recirculated,.and therefore only makeup quantities of this halide are necessary for'the practice of my over-all process. The only reagent whichis consumed in this over-all process is the metal sulfide, and it will be seen that this sulfide is converted by my process to the transition metal and to a sulfur halide or to-sulfur.

The disproportionation reaction is made to take place at normal pressure by heating the lower valent transition metal halide to a temperature about 500 C., and preferably more, above the lower. limit for producing the lower halide by reaction of. the corresponding. higher valent halide with the sulfide. However, the disproportionation reactionmay be madeto proceed effectively at significantly lower temperature by lowering the pressure inthe re action zone. For example, the reaction between titanium tetrachloride and titanium sulfide at atmospheric pressure proceeds readily at a temperature within the range of 500-800 C. to form titanium trichloride. The titanium trichloride can be readilyvdisproportionated. to a mixture of titanium dichloride and titanium tetrachloride at a temperature of 660 C. by lowering the reaction zone pressure to about 0.5 mm. of mercury. If a higher vacuum of about mm. of mercury is used, this disproportionation reaction takes place effectively attemperatures as low as 500 C. The final disproportionation of titanium dichloride to metal and to titanium tetrachloride takes place within the range of 700800 C. in a vacuum of about 10- mm. of mercury but. requires a somewhat higher temperature at normalatmospheric pressure.

The reaction vessel in which the disproportionation is carried out may be lined with silicav or other material which is inert with respect to the reactants and reaction products. Where the disproportionation reaction is carried out at temperatures below about 800850 C., a graphite-lined reaction vessel is suitable. However, if higher reaction temperatures are used, the reaction. vessel may be lined with a substantially 100% dense fluoride of an alkaline earth metal. Another suitable construction material for use at high temperatures is the sulfide of one of the transition metals provided that it, too, is in a substantially 100% dense form or is in a well-sintered though less dense form in which it will not react with the transition metal halides.

The following examples are illustrative of the over-all process" forconverting one ofthe aforementioned transition metal sulfides-to the formof the-metal itself:

one of its higher valent states.

Example V The reactor consisted of a long silica tube sealed at both ends with vacuum-tight fittings. At one end provision was made for distillation of titanium tetrachloride into the tube, and at the other end there'was an exit leading to a condenser. Provision was made for evacuation of the system. A boat containing 200 gms, of minus 200' mesh high purity titanium monosulfide was placed in the center'of the tube. The'tube' was evacuated, purged with argon and then re-evacuated. Titanium tetrachloride at substantially atmospheric pressure was distilled into the furnace which was maintained at a temperature of about 650 C. The product halide sublimed in' the reaction zone and recrystallized in the cooler portion of the tube. After reaction had proceeded for several hours, the titanium tetrachloride flow was terminated and the reactor was evacuated to 10" atmospheres. The temperature of the furnace was-then raised to about 900 CL, following which it was cooled under vacuum. Fine particles" of titanium metal were deposited on the walls of the tube. V

Example VI The reaction was run as indicated in Example V using zirconium tetrabromide and zirconium sulfide as reactants. The temperature range used in this case was about 650 C. in the reducing reaction and about 800 C. in the sec 0nd or disproportionation reaction. powder was thus produced.

Although the practice of the invention has been described and illustrated hereinbefore for the production of the lower valent halides of a single polyvalent transition metal, as well as for the production of the individual metal itself, the process of' the invention is equally ap plicable to the production of lower valent halides of a mixture of transition metals and, hence, to the production of mixtures or alloys of these transition metals. This result can be achieved by the use of either'a mixture of the higher valent halides of two or more transition metals or of the sulfides of two or more transition metals, or by a combination of these procedures. The final metallic product can therefore be either the substantially pure transition metal itself or a mixture of two or more of these metals.

Furthermore although the foregoing specification has exemplified the preparation of lower valent halides ofthe several polyva'lent transition metals by reaction between their simple higher valent halides (e. g. rrcn, ZrCl VCl VF and their simple sulfides, it is to be noted that similar reactions may be effected between the simple sulfides and the complex higher valent halides of these metals, such as the double halides of the transition metal and an1alkali metal, in which the transition metal exhibits Thus K TiCl Na TiCl- K T1F or Na TiF or other suitable complex tetraha'l'ides of titanium may be substituted for the TiCl, of Examples I or II, with similar results. Or complex titanium-alkali metal-bromides and complex zirconium halides in which the zirconium is tetravalent may be substituted in Examples III and IV without materially changing the processes disclosed.

It is also possible to carry out the same reactions (with 'little or no change in the reaction conditions) between complex halides of the polyvalent transition metals and complex sulfides of the transition metals to produce loweu valent simple or complex halides of the metals whichmay be recovered as fused salt compositions or which may-be disproportionated to obtain the metals themselves in the manner taught in Examples V and VI above.

Accordingly, in the following claims the terms halide and sulfide are intended to include both the simpleand complex transition metal halides or sulfides as the case may be, unless designated as one or .the other, specifically;

Zirconium metal I claim:

1. The method of producing lower valent halides of a metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum which comprises bringing a higher valent halide vapor of one of said metals into contact with a lower valent sulfide of the same metal in the form of particles at least as fine as about 200 mesh, the valence of the metal in the lower valent sulfide being no higher than the valence of the metal in the resulting lower valent halide product, and effecting reaction between said metal halide vapor and metal sulfide by maintaining the reactants at a temperature at .least as high as the volatilization temperature of said higher valent metal halide but below that at which the resulting lower valent metal halides disproportionate to the metal itself.

2. The method of producing lower valent halides of a metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum which comprises bringing a higher valent halide vapor of one of said metals into contact with a lower valent sulfide of the same metal in the form of particles at least as fine as about 200 mesh, the valence of the metal in the lower valent sulfide being no higher than the valence of the metal in the resulting lower valent halide product, and effecting reaction between said metal halide vapor and metal sulfide by maintaining the reactants at a temperature within the range of about 300 to 1100 C. which is at least as high as the volatilization temperature of said higher valent metal halide but below that at which the resulting lower valent metal halides disproportionate to the metal itself.

3. The method of producing lower valent halides of a metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum which comprises bringing a higher valent halide vapor of one of said metals into contact with a lower valent sulfide of the same metal in the form of particles at least as fine as about 200 mesh, the valence of the metal in the lower valent sulfide being no higher than the valence of the metal in the resulting lower valent halide product, and effecting reaction between said metal halide vapor and metal sulfide by maintaining the reactants at subatmospheric pressure and at a temperature at least as high as the volatilization temperature of said higher vlaent metal halide but below that at which the resulting lower valent metal halides disproportionate to the metal itself at said subatmospheric pressure.

4. The method of producing lower valent halides of titanium which comprises: bringing a higher valent titanium halide vapor into contact with a titanium sulfide in which the valence of the titanium is no higher than the valence of the titanium in the lower valent titanium halide produced and which is in the form of particles at least as fine as about 200 mesh, effecting reaction between said titanium halide vapor and said sulfide by maintaining the reactants at a temperature at least as high as the volatilization temperature of said higher valent titanium halide but below that at which the resulting lower valent titanium halides disproportionate to the metal itself.

5. The method of producing a metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum which comprises: bringing a higher valent halide vapor of one of said metals into contact with a lower valent sulfide of the same metal in the form of particles at least as fine as about 200 mesh, the valence of the metal in the lower valent sulfide being no higher than the valence of the metal in the resulting lower valent halide product, effecting reaction between said metal halide vapor and said metal sulfide by maintaining the reactants at a temperature at least as high as the volatilization temperature of said higher valent metal halide but below that at which the resulting lower valent metal halide disproportionates to the metal itself, and thereafter heating the resulting lower valent metal halide to a temperature at which it disproportionates to the metal itself. i

6. The method of producing lower valent halides of titanium which comprises: bringing a higher valent titanium halide vapor into contact with a titanium sulfide in which the valence of the titanium is no higher than the valence of the titanium in the lower valent titanium halide produced and which is in the form of particles at least as fine as about 200 mesh, effecting reaction between said titanium halide vapor and said sulfide by maintaining the reactants at subatmospheric pressure and at a temperature which is at least as high as the volatilization temperature of said higher valent titanium halide but below that at which the resulting lower valent metal halides disproportionate to the metal itself.

7. The method of producing a metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium vand tantalum which comprises: bringing a higher valent halide vapor of one of said metals into contact with a lower valent sulfide of the same metal in the form of particles at least as fine as about 200 mesh, the valence of the metal in the lower valent sulfide being no higher than the valence of the metal in the resulting lower valent halide product, effecting reaction betweei said halide vapor and said sulfide by maintaining tl reactants at subatmospheric pressure and at. a temperature at least as high as the voltalization temperature of said higher valent metal halide but below that at wlrich the resulting lower valent metal halide disproportiorates to the metal itself at said subatmospheric pressure. and thereafter heating the resulting lower valent metal halide to a temperature at which it disproportionates to the metal itself.

8. The method of producing lower valent halides of a metal of the group consisting of titanium, zirconium, hafnium, vanadium, niobium and tantalum which com prises: bringing a higher valent halide vapor of one of said metals into contact with a lower valent-sulfide of the same metal in the form of particles at least as fine as about 200 mesh, the valence of the metal in the lower valent sulfide being no higher than the valence of the metal in the resulting lower valent halide product, effecting reaction between said higher valent metal halide and said lower valent sulfide by maintaining the reactants at a temperature at least as high as the volatilization temperature of said higher valent metal halide, but below that at which the resulting lower valent metal halide disproportionates to themetal itself, leaching the reaction mass with carbon disulfide to remove free sulfur and soluble sulfur containing reaction products, and recovering the lower valent halide product.

9. The method of producing lower valent halides of titanium which comprises: bringing a higher valent titanium halide vapor into contact with a lower valent sulfide titanium in the form of particles at least as fine as about 200 mesh, and effecting reaction between said higher valent titanium halide and lower valent sulfide by maintaining the reactants at a temperature at least as high as the volatilization temperature of said higher valent titanium halide but below that which the resulting lower valent metal halide disproportionates to titanium itself, leaching the reaction products with carbon disulfide to remove sulfur and sulfur containing reaction products, and recovering the lower valent halide of titanium.

10. The method of producing titanium dihalides which comprises: bringing a titanium tetrahalide vapor into contact with titanium monosulfide in the form of particles at least as fine as about 200 mesh, effecting reaction between said tetrahalide vapor and said sulfide by maintaining the temperature of the reactants between about 300 C. and 800 C. and recovering the titanium dihalide from the reaction products. 1

11. The method of producing titanium trihalides which comprises:' bringing a titanium tetrahalide vapor into contact with titanium sulfide from the group consisting of titanium monosulfide and titanium sesquisulfide in the form of particles at least as fine as about 200 mesh, efiecting reaction between said tetrahalide vapor and said sulfide by maintaining the temperature of the reactants between about 300 C. and 800 C. and recovering the titanium trihalide from the reaction products.

10 References Cited in the file of this patent UNITED STATES PATENTS Jordan Feb. 23, 1954 Gross et a1 Aug. 28, 1956 OTHER REFERENCES 

1. THE METHOD OF PRODUCING LOWER VALENT HALIDES OF A METAL OF THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM, NIOBIUM AND TANTALUM WHICH COMPRISES BRINGING A HIGHER VALENT HALIDE VAPOR OF ONE OF SAID METALS INTO CONTACT WITH A LOWER VALENT SULFIDE OF THE SAME METAL IN THE FORM OF PARTICLES AT LEAST AS FINE AS ABOUT 200 MESH, THE VALENCE OF THE METAL IN THE LOWER VALENT SULFIDE BEING NO HIGHER THAN THE VALENCE OF THE METAL IN THE RESULTING LOWER VALENT HALIDE PRODUCT, AND EFFECTING REACTION BETWEEN SAID METAL HALIDE VAPOR AND METAL SULFIDE BY MAINTAINING THE REACTANTS AT A TEMPERATURE AT LEAST AS HIGH AS THE VOLATIZATION TEMPERATURE OF SAID HIGHER VALENT METAL HALIDE BUT BELOW THA AT WHICH THE RESULTING LOWER VALENT METAL HALIDES DISPROPORTIONATE TO THE METAL ITSELF. 